Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce dopant impurities into semiconductor wafers. Generally speaking, with respect to semiconductor applications, ion implantation involves the introduction of ions from a dopant species, also commonly referred to as dopant impurities, into a semiconductor substrate material in order to change the substrate material's physical, chemical and/or electrical characteristics. The desired dopant impurities are introduced into semiconductor wafers to form doped regions at a desired depth. The dopant impurities are selected to bond with the semiconductor wafer material to create electrical carriers and thereby alter the electrical conductivity of the semiconductor wafer material. The concentration of dopant impurities introduced determines the electrical conductivity of the doped region. Many impurity regions are necessarily created to form transistor structures, isolation structures and other electronic structures, which collectively function as a semiconductor device.
An ion source is used to generate a well-defined ion beam of ion species from the dopant species. The ion source is a critical component of the ion implantation system, which serves to ionize dopant species that are to be implanted during the implantation process. The dopant ions are generally derived from a source dopant species. The ion-source generates a defined ion beam for a variety of ion species derived from a source dopant gas. The ion source can be a filament or cathode made of tungsten (W) or tungsten alloy. Current is applied to the filament to ionize the source dopant species within an ion implanter. The source dopant species dissociates into corresponding ionic species, which is thereafter implanted into a given substrate.
Current semiconductor device technology utilizes a variety of dopant species. In specific applications, implantation of selenium (Se) ions into specific sections or regions of the semiconductor wafer has emerged as a widely used dopant introduction method to enhance device function. For example, Se implantation onto silicide contacts is reported to reduce the contact resistance in nMOS devices and improve its performance.
Today, the industry utilizes Se-containing solid sources in the form of Se metal or SeO2 for ion implantation. However, numerous process challenges currently exist for effective implantation of Se ions utilizing Se-containing solid sources. In particular, the solid sources require a vaporizer assembly and sufficient heating of the solid to generate Se containing vapors with sufficient vapor pressure to allow transport of the vapors to the ion-source assembly. However, the solid sources exhibit poor flow control that prevents stable operation. Additionally, adequate start-up time is required for the vaporizer assembly to be heated to the desired temperature before the user can start the Se implant process. Similarly, downtime must be allowed and taken into consideration for sufficient cool down to occur upon completion of the Se implant process. The extended time requirements when utilizing solid sources can result in significant productivity losses.
In view of the problems associated with solid precursors, Se-containing gas sources have been utilized. H2Se is a commonly known gas source for Se implant. However, the applicants observed that utilizing H2Se produces Se containing deposits inside the ion implantation equipment that can result in short ion source life. As a result, ion source maintenance is required at very frequent intervals, which results in ion implanter down-time and reduced production time.
As an alternative, SeO2 has been utilized. However, the presence of oxygen can lead to oxygen poisoning, which can lead to limited or shortened source life during selenium ion implantation.
Furthermore, Se precursor dopant materials are toxic to humans and therefore handling of Se precursor materials must be performed carefully to prevent exposure via contact or inhalation. Many of the precursor Se dopant materials used for the supply of Se species to be ionized in the ion source are toxic. The handling of such materials must be done carefully to prevent exposure and minimizing the quantity of such materials to be handled is valuable.
There currently is no viable dopant source to perform Se ion implantation given its shortcomings. Accordingly, there is an unmet need to extend the time between maintenance cycles for the ion source as well as to limit the quantity of Se dopant material that is required to allow for ion implantation in a safe and reliable manner during Se ion implantation.